1. Field of the Invention
The present invention relates to a damper pressure control apparatus for a hydraulic rock drill for crushing a rock or the like by striking a tool, such as a rod, chisel or the like.
2. Description of the Related Art
As shown in FIG. 8, in which is illustrated one of typical conventional hydraulic rock drills, a shank rod 102 is mounted at the front end of a hydraulic rock drill body 101. A hole boring bit 106 is mounted on the front end of a rod 104 via a sleeve 105. When a striking piston 107 of a striking mechanism 103 of the hydraulic rock drill strikes the shank rod 102, a striking energy is transmitted to the bit 106 from the shank rod 102 via the rod 104. Then, the bit 106 strikes a rock R to crush.
At this time, a reaction energy Er from the rock R is transmitted to the hydraulic rock drill body 101 from the bit 106 via the rod 104 and the shank rod 102. By the reaction energy Er, the hydraulic rock drill body 101 is driven backward once. Then, the hydraulic rock drill body 101 is propelled by a thrust of a feeding device (not shown) for a crushing length in one strike from a position before striking. Then, at the advanced position, next strike is performed by the striking mechanism 103. By repeating these steps, hole boring operation is performed.
Then, as a damping mechanism of the rock drill, namely a mechanism for damping the reaction energy Er, there have been developed a mechanism employing a two stage damping piston having a function for hydraulically damping the reaction energy Er and a function for improving striking transmission efficiency (dual damper type), and a mechanism employing a single damping piston which is not mechanically fixed the position thereof (floating type).
In FIG. 9 the hydraulic rock drill employing the two stage damping piston is provided with a chuck driver 109 applying rotation for the shank rod 102 via a chuck 108. For the chuck driver 109, a chuck driver bushing 110 is fitted as a transmission member contacting with a large diameter rear end 102a of the shank rod 102. Then, on the backside of the chuck driver bushing 110, a front damping piston 111 and a rear damping piston 112 are arranged as a damping mechanism.
The rear damping piston 112 is a cylindrical piston having a fluid passage 113 communicating outside and inside thereof. The rear damping piston 112 is slidably mounted between a central step portion 101c and a rear step portion 101b provided in the hydraulic rock drill body 101. The rear damping piston 112 is applied a frontward thrust by a hydraulic pressure in a fluid chamber 114 for the rear damping piston. On the other hand, the front damping piston 111 is a cylindrical piston having a small external diameter at the rear portion. The small diameter portion of the front damping piston 111 is inserted within the rear damping piston 112 in longitudinally slidable fashion. By a large diameter portion, the front damping piston 111 is restricted a longitudinal motion range between a front side step portion 101a of the hydraulic rock drill body 101 and a front end face 112a of the rear damping piston 112. Between an outer periphery of the small diameter portion of the front damping piston 111 and an inner periphery of the rear damping piston 112, a fluid chamber 115 for the front damping piston is defined for applying a frontward thrust to the front damping piston 111.
The fluid chamber 115 for the front damping piston and the fluid chamber 114 for the rear damping piston are communicated through a fluid passage 113. The fluid chamber 114 of the rear damping piston is communicated with a hydraulic pressure source 116. A hydraulic pressure from the hydraulic pressure source 116 is fixed at a given pressure by a relief valve or pressure reduction valve (not shown). To the front damping piston 111, a given thrust F111 derived as a product of a pressure receiving area and a hydraulic pressure in the fluid chamber 115 of the front damping piston, acts. Similarly, to the rear damping piston 112, a given thrust F112 derived as a product of a pressure receiving area and a hydraulic pressure in the fluid chamber 114 for the rear damping piston, acts.
On the other hand, to the hydraulic rock drill body 101, a frontward thrust F101 is constantly applied. This thrust is transmitted to the front damping piston 111 and the rear damping piston 112 as reaction force from the rock R via the bit 106, the rod 104, the shank rod 102 and the chuck driver bushing 110.
Here, the thrust F111 acting on the front damping piston 111 and the thrust F112 acting on the rear damping piston 112 are set relative to the thrust F101 acting on the hydraulic rock drill body 101 to establish a relationship F111&lt;F101&lt;F112. Therefore, before striking, the front damping piston 111 and the rear damping piston 112 contact with each other to stop at striking reference position (position shown in FIG. 9) where the front end face 112a of the rear damping piston 112 contacts with the central step portion 101c of the hydraulic rock drill body 101.
At the striking reference position, when the striking piston 107 of the striking mechanism 103 strikes the shank rod 102, the striking energy is transmitted from the shank rod 102 to the bit 106 via the rod 104. Then, the bit 106 strikes the rock R as crushing object. At this time, the reaction energy Er from the rock R is transmitted to the front damping piston 111 and the rear damping piston 112 from the bit 106 via the rod 104, the shank rod 102 and the chuck driver bushing 110. Then, the rear damping piston 112 is retracted until contacting the rear end face with a rear step portion 101b together with the front damping piston 111 with damping by the thrust F112. Thus, the reaction energy Er is transmitted to the hydraulic rock drill body 101. Accordingly, the rear damping piston 112 performs damping function of the reaction energy Er, namely impact force absorbing function. Also, the thrust acting on the rear damping piston 112 serves as damping force.
By the reaction energy Er transmitted to the hydraulic rock drill body 101, the main body 101 is driven backward once. Subsequently, the rear damping piston 112 is driven forward to stop at the striking reference position where the front end face 112a thereof abuts onto the central step portion 101c of the hydraulic rock drill body 101 by pushing back the front damping piston 111, the chuck driver bushing 110 and the shank rod 102 since the thrust F112 applied by the fluid pressure in the fluid chamber 114 for the rear damping piston is greater than the thrust F101 applied to the hydraulic rock drill body 101. At this condition, the next striking is awaited.
In the condition where contact between the bit 106 and the rock R is incomplete, the thrust F101 of the hydraulic rock drill body 101 is not sufficiently transmitted to the rock R. Therefore, a reaction force much smaller than the thrust F101 is transmitted to the rod 104, the sleeve 105, the shank rod 102, the chuck driver bushing 110 and the front damping piston 111 from the bit 106. Accordingly, the front damping piston 111 is moved away from the rear damping piston 112 by the thrust F111 to urge the bit 106 toward the rock R via the chuck driver bushing 110 and the shank rod 102 to advance the bit 106 before advancement of the hydraulic rock drill body 101 to prevent blank striking. Accordingly, the front damping piston 111 performs action for tightly contacting the tool, such as bit 106 or the like onto the rock R, namely, floating action. Then, the thrust F111 on the front damping piston 111 serves as floating force.
Subsequently, the hydraulic rock drill body 101 is advanced by the thrust F101. After contacting the bit 106 onto the rock R, since the thrust F101 of the hydraulic rock drill body 101 is greater than the thrust F111 of the front damping piston 111, the front damping piston 111 is pushed back until it comes in contact with the rear damping piston 112.
On the other hand, as shown in FIG. 10, in the case of a floating system using a single damping piston which is not mechanically fixed in position, the hydraulic rock drill body 101 is provided with a chuck driver 109 applying a rotational force of the shank rod 102 via the chuck 108. To the chuck driver 109, the chuck driver bushing 110 is mounted as a transmission member contacting with a large diameter rear end 102a of the shank rod 102. On the rear side of the chuck driver bushing 110, a damping piston 130 forming as damping mechanism is provided.
The damping piston 130 is a cylindrical piston which has large diameter portion 130a at front side and a small diameter portion 130b at rear side. Between the large diameter portion 130a and the small diameter portion 130b, a neck portion 130c having external diameter smaller than the small diameter portion 130b is provided. The damping piston 130 is slidably inserted within the hydraulic rock drill body 101 for longitudinal movement between a front step portion 101a and a rear step portion 101b.
Between an inner peripheral sliding surface of the hydraulic rock drill body 101 and the neck portion 130c of the damping piston 130, a hydraulic pressure chamber 131 is defined. The damping piston 130 is applied a forward thrust by the hydraulic pressure in the hydraulic pressure chamber 131. On the inner peripheral sliding surface of the hydraulic rock drill body 101, a drain passage 133 is defined at the front side of the hydraulic pressure chamber 131 at a position distant from the latter for a seal length S1, and a pressure supply passage 132 is defined at the rear side of the hydraulic pressure chamber 131 at a position distant from the latter for a seal length S2. The pressure supply passage 132 is communicated with a hydraulic pressure source 116.
A hydraulic pressure P2 applied to the damping piston 130 from the hydraulic pressure source 116 is fixed at a given pressure by a relief valve or a pressure reduction valve (not shown) similarly to the case when the two stage damping piston is used.
A pressurized fluid from the hydraulic pressure source 116 flows into the hydraulic pressure chamber 131 via the pressure supply passage 132 and the seal length S2 and is discharged to the drain passage 133 via the seal length S1. At this time, a pressure P1 as a difference between inflow amount and flow-out amount of the pressurized fluid is generated within the hydraulic pressure chamber 131. The pressure P1 of the hydraulic pressure chamber 131 is smaller than a hydraulic pressure P2 from the hydraulic power source 116, and thus P1&lt;P2 is established.
The thrust F130 to be applied to the damping piston 130 is a product of a pressure receiving area of the hydraulic pressure chamber 131 and the pressure P1 and a thrust to be applied to the hydraulic rock drill body 101 by a known feeding mechanism is assumed as F101. The thrust F130 is set to be equal to the thrust F101 in the condition where the damping piston 130 is stopped at the striking reference position (position shown in FIG. 10).
When the damping piston 130 is retracted from the striking reference position, the seal length S2 is reduced to increase flow amount of the pressurized fluid flowing into the hydraulic pressure chamber 131 from the hydraulic pressure source 116 via the pressure supply passage 132, and conversely, the seal length S1 is increased to reduce flow amount of the pressurized fluid from the hydraulic pressure chamber 131 to the drain passage 133. By this, the hydraulic pressure P131 in the hydraulic pressure chamber 131 is increased to increase frontward thrust F130 applied to the damping piston 130.
Furthermore, when the damping piston 130 is driven backward to contact the rear end face 130e of the damping piston 130 onto the rear step portion 101b, the seal length S2 becomes smaller than or equal to 0. Then, all amount of the pressurized fluid from the hydraulic pressure source 116 flows into the hydraulic pressure chamber 131, and conversely, the seal length S1 is further increased to further reduce pressurized fluid flowing out to the drain passage 133. By this, the hydraulic pressure P1 in the hydraulic pressure chamber 131 is further increased. Therefore, forward thrust F130 to be applied to the damping piston 130 becomes maximum.
On the other hand, when the damping piston 130 is advanced from the striking reference position, the seal length S2 is increased to reduce the flow amount of the pressurized fluid flowing into the hydraulic pressure chamber 131 via the pressure supply passage 132, and conversely, the seal length S1 is reduced to increase flow amount flowing out from the hydraulic pressure chamber 131 to the drain passage 133. By this, the hydraulic pressure P1 in the hydraulic pressure chamber 131 is reduced to reduce the frontward thrust F130 to be applied to the damping piston 130.
When the damping piston 130 is further advanced to contact the front end face 130d onto the front step portion 101a, the seal length S1 becomes smaller than or equal to 0. Then, the hydraulic pressure chamber 131 and the drain passage 133 are communicated to further reduce the hydraulic pressure P1 in the hydraulic pressure chamber 131. Therefore, the forward thrust F130 to be applied to the damping piston 130 becomes minimum.
In the striking reference position, the striking piston 107 strikes the shank rod 102. Then, the striking energy is transmitted to the bit 106 from the shank rod 102 via the rod 104 to strike and crush the rock R as crushing object by the bit 106.
At this time, the reaction energy Er instantly generated from the rock R is transmitted to the damping piston 130 from the bit 106 via the shank rod 102 and the chuck driver bushing 110. The damping piston 130 is driven backward as being damped by the hydraulic pressure of the hydraulic pressure chamber 130. Then, the reaction energy Er is transmitted to the hydraulic rock drill body 101.
Accordingly, the damping piston 130 performs damping action of the reaction energy Er, namely impact force absorbing action. Then, the thrust F130 acting on the damping piston 130 serves as the damping thrust.
By the reaction energy Er transmitted to the hydraulic rock drill body 101, the hydraulic rock drill body 101 is driven backward once. Subsequently, the reaction force against the striking force is reduced. Then, the reaction force to act on the chuck driver bushing 110 becomes only reaction force of the thrust F101 to be applied to the hydraulic rock drill body 101. On the other hand, associating with backward motion of the damping piston 130, the hydraulic pressure P1 in the hydraulic pressure chamber 131 is increased. Then, the forward thrust F130 acting on the damping piston 130 becomes greater than the thrust F101 applied to the hydraulic rock drill body 101. Therefore, the damping piston 130 is advanced frontward up to the striking reference position with pushing back the chuck driver bushing 110 and the shank rod 102. Then, the forward thrust F130 acting on the damping piston 130 becomes equal to the reaction force of the thrust F101 applied to the hydraulic rock drill body 101 to stop the damping piston 130.
During this, the hydraulic rock drill body 101 is advanced for crushing length of the rock R in one strike by the feeding mechanism to contact the bit 106 onto the rock R. When the bit 106 comes in contact with the rock R, the thrust F101 of the hydraulic rock drill body 101 is transmitted from the bit 106 to the damping piston 130 as reaction force. Then, the damping piston 130 is held at a position where the frontward thrust F130 acting on the damping piston 130 becomes equal to the thrust F101 of the hydraulic rock drill body 101, namely at the striking reference position to be situated in the condition waiting next strike.
In the condition where contact between the rock R and the bit 106 is incomplete, the thrust F101 of the hydraulic rock drill body 101 is not sufficiently transmitted to the rock R. Thus, from the bit 106, the reaction force much smaller than the thrust F130 is applied to the rod 104, the sleeve 105, the chuck driver bushing 110 and the damping piston 130. At this time,the damping piston 130 is advanced frontward from the striking reference position and stops at the position where the reaction force F101 and the forward thrust F130 applied to the damping piston 130 become equal to each other. Accordingly, the damping piston 130 acts for firmly contacting the tool, such as rod 104, the bit 106 and so forth onto the rock R, namely floating function. Then, the thrust F130 acting on the damping piston 130 serves as the floating force.
In such damping mechanisms of these hydraulic rock drills, the damping piston per se performs function to urge the tool such as the bit 106 or the like onto the rock R with higher sensitivity than forward thrust acting on the hydraulic rock drill body 101, namely the damping piston 130 achieves function to firmly contact the tool onto the rock R. Therefore, it becomes necessary to adjust a damping pressure from the hydraulic power source to be applied to the damping piston similarly to a feeding pressure to be applied to the hydraulic rock drill body 101 which is adjusted by hole boring condition.
The damping mechanism shown in FIG. 9 employs the two stage damping piston.
As set forth above, the rear damping piston 112 performs damping function of the reaction energy Er, namely shock absorbing function, and the front damping piston 111 performs function to firmly contacting the tool, such as rod 104, bit 106 or the like onto the rock R, namely floating function. Then, in order to smoothly perform damping function and floating function, the floating force F111 acting on the front damping piston 111 and the damping force F112 acting on the rear damping piston 112 are set relative to the thrust F101 acting on the hydraulic rock drill body 101 to satisfy the relationship of F111&lt;F101&lt;F112.
However, the thrust F101 actually acting on the hydraulic rock drill body 101 is varies depending upon property of the rock R. For example, if the rock R is soft rock (fracture zone), the thrust F101 becomes low. Conversely, in the case of hard rock, the thrust F101 becomes high. This variation of thrust is referred to as Fv101.
On the other hand, since the hydraulic pressure source 116 is common, the floating force F111 and the damping force F112 can always maintain (F112/f111) or (F112-F111) constant.
Here, when the thrust Fv101 of the hydraulic rock drill body 101 is varied, the relationship between the floating force F111, the damping force F112 and the thrust Fv101 can be Fv101&lt;F111&lt;F112 (when the rock R is soft rock (fracture zone) or F111&lt;F112&lt;Fv101 (when the rock R is hard rock). When Fv101&lt;F111&lt;F112 is established, after contacting the bit 106 to the rock R, the front damping piston 111 is not pushed back until it comes in contact with the rear damping piston 112 to possibly cause floating failure. On the other hand, when F111&lt;F112&lt;Fv101 is established, since the rear damping piston 112 constantly abuts onto the rear step portion 101b, damping failure can be caused. Therefore, floating function and damping function becomes unsatisfactory.
On the other hand, when F111&lt;F112&lt;Fv101 is established, since the thrust acting on the rear damping piston 112 is smaller than the thrust of the hydraulic rock drill body 101, the shank rod 102 is retracted beyond the striking reference position. Therefore, upon striking of the shank rod 102 by the striking piston 107, the piston speed of the striking piston 107 does not become maximum to reduce striking force in spite of the fact that high striking is required essentially.
Even in the case of the floating type employing the single damper piston, the position of the damping piston 130 is varies depending upon property of the rock R. This variation of the position of the damping piston appears more significantly in the case of the floating type employing the single damping piston.